Wafer inspection based on electron beam induced current

ABSTRACT

A wafer inspection system is disclosed. According to certain embodiments, the system includes an electron detector that includes circuitry to detect secondary electrons or backscattered electrons (SE/BSE) emitted from a wafer. The electron beam system also includes a current detector that includes circuitry to detect an electron-beam-induced current (EBIC) from the wafer. The electron beam system further includes a controller having one or more processors and a memory, the controller including circuitry to: acquire data regarding the SE/BSE; acquire data regarding the EBIC; and determine structural information of the wafer based on an evaluation of the SE/BSE data and the EBIC data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application No.PCT/EP2019/063286, filed May 23, 2019, and published as WO 2019/238373A1, which claims priority of U.S. application 62/684,141 which was filedon Jun. 12, 2018. The contents of these applications are incorporatedherein by reference in their entireties.

TECHNICAL FIELD

The present disclosure generally relates to the field of semiconductorwafer metrology, and more particularly, to a system and method forinspecting a wafer by coupling secondary-electron/backscattered-electron(SE/BSE) imaging of the wafer with electron-beam-induced-current (EBIC)imaging of wafer.

BACKGROUND

In manufacturing processes of integrated circuits (ICs), unfinished orfinished circuit components need to be inspected to ensure that they aremanufactured according to design and are free of defects. Moreover,before being used to fabricate the ICs, an un-patterned or bare waferalso needs to be inspected to ensure it is free of defects or meets therequired specifications. As such, a wafer inspection process has beenintegrated into the manufacturing process. Specifically, a waferinspection system may employ optical microscopies or a charged particle(e.g., electron) beam microscopes, such as a scanning electronmicroscope (SEM), to scan a wafer and construct an image of the wafersurface. The wafer inspection system may then examine the image todetect defects and determine their position coordinates on the wafer.

Compared to a photon beam, an electron beam has a shorter wavelength andthereby may offer superior spatial resolution. Typically, an SEM mayfocus electrons of a primary electron beam at predetermined scanlocations of a wafer under inspection. The primary electron beaminteracts with the wafer and may be backscattered or may cause the waferto emit secondary electrons. The intensity of the backscattered orsecondary electrons may vary based on the properties of the internal orexternal structures of the wafer, and thus indicates structuralinformation of the wafer, such as defects on the wafer, dimensions ofcertain features, etc.

SUMMARY

Embodiments of the present disclosure relate to a system for inspectinga wafer by coupling secondary-electron/backscattered-electron (SE/BSE)imaging of the wafer with electron-beam-induced-current (EBIC) imagingof the wafer. In some embodiments, an electron beam system is provided.The electron beam system includes an electron detector that includescircuitry to detect SE/BSE emitted from a wafer. The electron beamsystem also includes a current detector that includes circuitry todetect an EBIC from the wafer. The electron beam system further includesa controller having one or more processors and a memory, the controllerincluding circuitry to: acquire data regarding the SE/BSE; acquire dataregarding the EBIC; and determine structural information of the waferbased on an evaluation of the SE/BSE data and the EBIC data.

In some embodiments, a computer system is provided. The computer systemincludes a memory storing instructions. The computer system alsoincludes a processor electronically coupled to the memory. The processorincludes circuitry to execute the instructions to cause the computersystem to: acquire data regarding secondary electrons or backscatteredelectrons (SE/BSE) emitted from a wafer; acquire data regarding anelectron-beam-induced current (EBIC) from the wafer; evaluate the SE/BSEdata and the EBIC data; and determine structural information of thewafer based on the evaluation of the SE/BSE data and the EBIC data.

In some embodiments, a method is provided. The method includes:acquiring data regarding secondary electrons or backscattered electrons(SE/BSE) emitted from a wafer scanned with an electron beam; acquiringdata regarding an electron-beam-induced current (EBIC) from the wafer;and determining structural information of the wafer based on anevaluation of the SE/BSE data and the EBIC data.

In some embodiments, a non-transitory computer-readable medium isprovided. The medium stores a set of instructions that is executable byone or more processors of one or more devices to cause the one or moredevices to perform a method including: acquiring data regardingsecondary electrons or backscattered electrons (SE/BSE) emitted from awafer; acquiring data regarding an electron-beam-induced current (EBIC)from the wafer; and determining structural information of the waferbased on an evaluation of the SE/BSE data and the EBIC data.

Additional objects and advantages of the disclosed embodiments will beset forth in part in the following description, and in part will beapparent from the description, or may be learned by practice of theembodiments. The objects and advantages of the disclosed embodiments maybe realized and attained by the elements and combinations set forth inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosed embodiments, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an exemplary electron beaminspection (EBI) system, consistent with embodiments of the presentdisclosure.

FIG. 2 is a schematic diagram illustrating an exemplary electron beamtool that may be a part of the exemplary electron beam inspection ofFIG. 1, consistent with embodiments of the present disclosure.

FIG. 3 is a schematic diagram illustrating a structural configurationfor measuring EBIC, consistent with embodiments of the presentdisclosure.

FIG. 4 is a schematic diagram illustrating coupling of SE/BSEmeasurement with EBIC measurement, consistent with embodiments of thepresent disclosure.

FIG. 5 is a schematic diagram illustrating correlation between a wafer'sSE/BSE signal and EBIC signal, consistent with embodiments of thepresent disclosure.

FIG. 6 is a block diagram of an exemplary controller in communicationwith the electron beam inspection of FIG. 2, consistent with embodimentsof the present disclosure.

FIG. 7 is a flowchart of a wafer inspection method, consistent withembodiments of the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings. The followingdescription refers to the accompanying drawings in which the samenumbers in different drawings represent the same or similar elementsunless otherwise represented. The implementations set forth in thefollowing description of exemplary embodiments do not represent allimplementations consistent with the invention. Instead, they are merelyexamples of apparatuses and methods consistent with aspects related tothe invention as recited in the appended claims.

As described above, typical electron-beam (ebeam) tools (e.g., SEM) relyon backscattered or secondary electrons to detect structure informationof a wafer. However, often in practice the wafer is made from materialthat can only emit few backscattered or secondary electrons. Moreover,the wafer may be patterned with structures that impair the wafer'sability to emit the backscattered or secondary electrons. In thesesituations, the backscattered/secondary-electron signal may be too weakto reveal information of any fine structures. Although spending moretime in scanning the wafer may increase the amount of collectedbackscattered/secondary electrons, this will deteriorate the throughputof the ebeam tools.

The present application provides an ebeam system for detecting waferstructure based on an electron signal other than, or in addition to, thebackscattered/secondary-electron signal. Some of the techniquesdisclosed herein solve the problems associated with the weakbackscattered/secondary-electron signal. In particular, when the waferis scanned by an electron beam, the wafer not only may emitbackscattered or secondary electrons, but also may release an electriccurrent. The intensity of the released electric current may also varybased on the properties of the internal or external structures of thewafer, and thus indicate structural information of the wafer. Thedisclosed ebeam system collects and analyses the released electriccurrent to determine the wafer structure information. As explained inmore detail below, the intensity of the released electric current ishigh when the backscattered/secondary-electron signal is weak.Therefore, the disclosed ebeam system can detect wafer structures thatthe traditional ebeam systems have difficulty in detecting. Moreover,the present application also provides techniques for simultaneouslycollecting the backscattered/secondary-electron signal and releasedcurrent signal, and comparing both signals to provide complementaryinformation about the wafer structure, without increasing the amount oftime for scanning the wafer. Therefore, the disclosed ebeam system candetect a wafer structure more accurately and efficiently.

As used throughout this application, unless specifically statedotherwise, the term “or” encompasses all possible combinations, exceptwhere infeasible. For example, if it is stated that a device can includeA or B, then, unless specifically stated otherwise or infeasible, thedevice can include A, or B, or A and B. As a second example, if it isstated that a device can include A, B, or C, then, unless specificallystated otherwise or infeasible, the device can include A, or B, or C, orA and B, or A and C, or B and C, or A and B and C.

FIG. 1 illustrates an exemplary electron beam inspection (EBI) system100 consistent with embodiments of the present disclosure. As shown inFIG. 1, EBI system 100 includes a main chamber 101, a load/lock chamber102, an electron beam tool 104, and an equipment front end module (EFEM)106. Electron beam tool 104 is located within main chamber 101. EFEM 106includes a first loading port 106 a and a second loading port 106 b.EFEM 106 may include additional loading port(s). First loading port 106a and second loading port 106 b receive wafer cassettes that containwafers (e.g., semiconductor wafers or wafers made of other material(s))or samples to be inspected (wafers and samples are collectively referredto as “wafers” hereafter).

One or more robot arms (not shown) in EFEM 106 transport the wafers toload/lock chamber 102. Load/lock chamber 102 is connected to a load/lockvacuum pump system (not shown) which removes gas molecules in load/lockchamber 102 to reach a first pressure below the atmospheric pressure.After reaching the first pressure, one or more robot arms (not shown)transport the wafer from load/lock chamber 102 to main chamber 101. Mainchamber 101 is connected to a main chamber vacuum pump system (notshown) which removes gas molecules in main chamber 101 to reach a secondpressure below the first pressure. After reaching the second pressure,the wafer is subject to inspection by electron beam tool 104.

FIG. 2 illustrates exemplary components of electron beam tool 104,consistent with embodiments of the present disclosure. As shown in FIG.2, electron beam tool 104 includes a motorized stage 200, and a waferholder 202 supported by motorized stage 200 to hold a wafer 203 to beinspected. Electron beam tool 104 further includes an objective lensassembly 204, electron detector 206 (which includes electron sensorsurfaces 206 a and 206 b), an objective aperture 208, a condenser lens210, a beam limit aperture 212, a gun aperture 214, an anode 216, and acathode 218. Objective lens assembly 204, in one embodiment, may includea modified swing objective retarding immersion lens (SORIL), whichincludes a pole piece 204 a, a control electrode 204 b, a deflector 204c, and an exciting coil 204 d. Electron beam tool 104 may additionallyinclude an energy dispersive X-ray spectrometer (EDS) detector (notshown) to characterize the materials on the wafer.

A primary electron beam 220 is emitted from cathode 218 by applying avoltage between anode 216 and cathode 218. Primary electron beam 220passes through gun aperture 214 and beam limit aperture 212, both ofwhich may determine the size of electron beam entering condenser lens210, which resides below beam limit aperture 212. Condenser lens 210focuses primary electron beam 220 before the beam enters objectiveaperture 208 to set the size of the electron beam before enteringobjective lens assembly 204. Deflector 204 c deflects primary electronbeam 220 to facilitate beam scanning on the wafer. For example, in ascanning process, deflector 204 c may be controlled to deflect primaryelectron beam 220 sequentially onto different locations of top surfaceof wafer 203 at different time points, to provide data for imagereconstruction for different parts of wafer 203. Moreover, deflector 204c may also be controlled to deflect primary electron beam 220 ontodifferent sides of wafer 203 at a particular location, at different timepoints, to provide data for stereo image reconstruction of the waferstructure at that location. Further, in some embodiments, anode 216 andcathode 218 may be configured to generate multiple primary electronbeams 220, and electron beam tool 104 may include a plurality ofdeflectors 204 c to project the multiple primary electron beams 220 todifferent parts/sides of the wafer at the same time, to provide data forimage reconstruction for different parts of wafer 203.

Exciting coil 204 d and pole piece 204 a may generate a magnetic fieldthat begins at one end of pole piece 204 a and terminates at the otherend of pole piece 204 a. A part of wafer 203 being scanned by primaryelectron beam 220 may be immersed in the magnetic field and may beelectrically charged, which, in turn, creates an electric field. Theelectric field reduces the energy of impinging primary electron beam 220near the surface of the wafer before it collides with the wafer. Controlelectrode 204 b, being electrically isolated from pole piece 204 a,controls an electric field on the wafer to prevent micro-arching of thewafer and to ensure proper beam focus.

A secondary-electron/backscattered-electron (SE/BSE) beam 222 may beemitted from the part of wafer 203 upon receiving primary electron beam220. Secondary electron beam 222 may form beam spot(s) on sensorsurfaces 206 a or 206 b of electron detector 206. Electron detector 206may generate a signal (e.g., a voltage, a current, etc.) that representsan intensity of the beam spot and may provide the signal to a controller300 via a wired or wireless communication with electron detector 206.The intensity of SE/BSE beam 222, and the resultant beam spot(s), mayvary according to the external or internal structure of wafer 203.Moreover, as discussed above, primary electron beam 220 may be projectedonto different locations of the top surface of the wafer, or differentsides of the wafer at a particular location, to generate SE/BSE beams222 (and the resultant beam spot) of different intensities. Therefore,by mapping the intensities of the beam spots with the locations of wafer203, controller 300 may reconstruct an SE/BSE image that reflects theinternal or external structures of wafer 203.

As described above, an ebeam tool offers superior spatial resolutionthan an optical tool. However, the ebeam tool's sensitivity stilldepends on the devices or structures to be detected. For example, somestructures, such as high-aspect-ratio (HAR) holes and trenches, mayprevent the backscattered electrons or secondary electrons from escapingthe wafer (e.g., wafer 203), thereby significantly reducing the amountof electrons reaching the detector (e.g., electron detector 206). Thisnot only makes different HAR structures appear dark in the SEM image,but also causes the SEM's signal-to-noise ratio to deteriorate. Forexample, there may be no difference for normal and defective HAR holesin an SEM image.

As in-line metrologies used in the semiconductor industry are beingchallenged by the aggressive pace of device scaling and the adoption ofnovel device architectures, the sensitivity limitations may keep theebeam tools from meeting the requirements posed by next-generation waferinspection technologies. For example, many different applications,including logic contacts, trench isolations, and three-dimensional (3D)memory features, require inspection to monitor the lithographicprocesses in creating HAR structures. For these applications, holes andtrenches of 20:1, 30:1, 40:1, or even 60:1 may need to be formed on awafer. For example, HAR contact holes may be 1 μm in depth and 30 nm indiameter, for an aspect ratio of approximately 30:1 at the 32 nm node.However, as explained above, medium or low energy backscatteredelectrons (BSE) and secondary electrons (SE) may have difficulty inescaping from HAR structures. Therefore, the BSE and SE basedmeasurement is less sensitive to HAR structures, and may miss importantdefect or critical-dimension information of HAR structures.

To solve these problems, electron beam tool 104 is further configured toobtain electron beam induced current (EBIC) of wafer 203, and determinethe structural information of wafer 203 based on the EBIC signal, inaddition to or in combination with the BSE/SE signal. Because somestructural features (e.g., HAR structures) may have a higher EBIC signalintensity than BSE/SE signal intensity, the EBIC signal is moresensitive to these structural features. Therefore, electron beam tool104's sensitivity is improved.

Specifically, consistent with the disclosed embodiments, wafer 203 maybe grounded via a wafer holder 202 and an EBIC detection circuit 230. Asschematically shown in FIG. 3, in some embodiments, an electric wire 231may be extended from wafer 203 and connected to the ground via sampleholder 202. While primary beam 220 scans wafer 203, the EBIC (orsubstrate current) may pass through electric wire 231 and be measured byEBIC detection circuit 230.

Referring back to FIG. 2, EBIC detection circuit 230 is in a wired orwireless communication with controller 300 and reports the measured EBICvalue to controller 300. As such, while primary electron beam 220 scanswafer 203, the SE/BSE and EBIC signals may be simultaneously measuredand transmitted to controller 300. Controller 300 may correlate theSE/BSE data and EBIC data that correspond to the same locations (orfeatures) of wafer 203. Controller 300 may also construct an SE/BSEimage and an EBIC image, respectively. For example, the SE/BSE image andEBIC image may be grayscale images whose grayscale levels areproportional to the intensities of the SE/BSE and EBIC signals.Controller 300 may further compare the SE/BSE data (or image) with theEBIC data (or image). Based on the comparison, controller 300 maydetermine structural information (e.g., defects, critical dimensions,edges, etc.) of wafer 203 that are not easy to be detected based on theSE/BSE data (or image) alone.

FIG. 4 is a schematic diagram illustrating the coupling of SE/BSEmeasurement and EBIC measurement, consistent with embodiments of thepresent disclosure. Referring to FIG. 4, the beam current of primaryelectron beam 220, I_(pe), may be measured by projecting primaryelectron beam 220 into a faraday cup (not shown). When primary electronbeam 220 is projected on surface of wafer 203, SE/BSE may be generatedand collected by electron detector 206. The current of the SE/BSE,l_(se/bse), is measured by electron detector 206 and amplified byamplifier 207. The amplified I_(se/bse) signal is then transmitted tocontroller 300. Meanwhile, EBIC is generated in the form of substratecurrent and flows to the ground. EBIC detection circuit 230 includes anammeter 232 (e.g., pico meter) for measuring the EBIC, I_(ebic), and anamplifier 233 for amplifying the I_(ebic) signal. The amplified I_(ebic)signal is then transmitted to controller 300. The I_(se/bse) signal andI_(ebic) signal may be used to contract the SE/BSE image and EBIC imagesof wafer 203, respectively. Because I_(pe)=I_(se/bse)+I_(ebic), whenI_(se/bse) is weaker due to certain features (e.g., materials, HARstructures, etc.) of wafer 203, l_(ebic) may be strong enough and may berelied upon to determine the structure information of wafer 203.

For example, the yield of SE/BSE emission may depend on the types ofmaterials coated on wafer 203.

-   -   Table 1 below shows the yield of SE/BSE emission

2.43 nA 4.9 nA SE/BSE SE/BSE I_(pe) I_(ebic) I_(se/bse) Yield I_(ebic)I_(se/bse) Yield Titanium (Ti)  2.4 nA 0.03 nA 0.01  4.8 nA  0.1 nA 0.02Gold (Au) 1.96 nA 0.47 nA 0.19 3.88 nA 1.02 nA 0.21

Referring to Table 1, I_(pe) and l_(ebic) may be measured by the faradaycup and ammeter 232, respectively. I_(se/bse) may be calculated based onI_(se/bse)=I_(pe)−l_(ebic) and the yield of SE/BSE emission may becalculated based on Yield=l_(se/bse)/I_(pe). As Table 1 indicates, heavymetals such as gold has relatively high yield of SE/BSE emission, whiletransition medals such as titanium has relatively low yield of SE/BSEemission. In the disclosed embodiments, when the wafer 203's yield ofSE/BSE emission is low, its l_(ebic) signal is strong and may be used todetermine structural information of wafer 203.

FIG. 5 is a schematic diagram illustrating correlation between SE/BSEsignal and

EBIC signal that are generated by the same wafer, consistent withembodiments of the present disclosure. Referring to FIG. 5, whileprimary electron beam 220 scans wafer 203, the SE/BSE signal and EBICsignal generated by wafer 203 may be synchronized. Depending on thespeeds (i.e., frequencies) of ammeter 232 and electron detector 206, theresolution of EBIC signal may be the same as or different from theresolution of the SE/BSE image. In the example shown in FIG. 5, theSE/BSE image of wafer 203 has a resolution of 2 nm, while the EBICsignal has a resolution of 1 μm, because ammeter 232 has a lower speedthan that of electron detector 206. As such, to compare the synchronizedSE/BSE signal and EBIC signal, the pixels of the SE/BSE image may befirst averaged over 1 μm and then compared with the EBIC signal.

As illustrated by FIG. 5, in the SE/BSE image, the pixels with highgrayscale values (i.e., “bright”) correspond to a lower I_(ebic), andthe pixels with low grayscale values (i.e., “dark”) correspond to ahigher I_(ebic). The line features on wafer 203 may be detected based onthe EBIC signal, SE/BSE signal, or a combination thereof.

FIG. 6 is a block diagram of an exemplary controller 300, consistentwith exemplary embodiments of the present disclosure. Controller 300 iselectronically connected to ebeam tool 104. Controller 300 may be acomputer configured to execute various controls of EBI system 100. Forexample, controller 300 may control various components of ebeam tool 104to scan primary electron beam 220 over the surface of wafer 203, suchthat wafer 203 may emit the SE/BSE and EBIC, which may be simultaneouslydetected by ebeam tool 104.

Referring to FIG. 6, controller 300 has a communication interface 322that is electrically coupled to ebeam tool 104 to receive the SE/BSEdata and EBIC data regarding a wafer. Controller 300 also includes aprocessor 324 that is configured to synchronize the SE/BSE data and EBICdata, construct an SE/BSE image and an EBIC image of the wafer, comparethe SE/BSE data/image with the EBIC data/image, and determine structuralinformation of the wafer based on the comparison.

Processor 324 may include one or more of a central processing unit(CPU), an image processing unit, an application-specific integratedcircuit (ASIC), a field-programmable gate array (FPGA), etc. In someembodiments, processor 324 may be one or more processing devicesdesigned to perform functions of the disclosed wafer inspection methods,such as a single core or multiple core processors capable of executingparallel processes simultaneously. For example, processor 324 may be asingle core processor configured with virtual processing technologies.In certain embodiments, processor 324 may use logical processors tosimultaneously execute and control multiple processes. Processor 324 mayimplement virtual machine technologies, or other known technologies toprovide the ability to execute, control, run, manipulate, store, etc.multiple software processes, applications, programs, etc. In someembodiments, processor 324 may include a multiple-core processorarrangement (e.g., dual core, quad core, etc.) configured to provideparallel processing functionalities to execute multiple processessimultaneously. It is appreciated that other types of processorarrangements could be implemented that provide for the capabilitiesdisclosed herein.

Controller 300 may also include memory 326 that includes instructions toenable processor 324 to execute one or more applications, such as thedisclosed wafer inspection processes, and any other type of applicationor software known to be available on computer systems. Alternatively oradditionally, the instructions, application programs, etc. may be storedin an internal database or an external storage (not shown) in directcommunication with controller 300. The internal database or externalstorage may be a volatile or non-volatile, magnetic, semiconductor,tape, optical, removable, non-removable, or other type of storage deviceor tangible or non-transitory computer-readable medium, or can be cloudstorage. Common forms of non-transitory media include, for example, afloppy disk, a flexible disk, hard disk, solid state drive, magnetictape, or any other magnetic data storage medium, a CD-ROM, any otheroptical data storage medium, any physical medium with patterns of holes,a RAM, a PROM, and EPROM, a FLASH-EPROM or any other flash memory,NVRAM, a cache, a register, any other memory chip or cartridge, andnetworked versions of the same.

Consistent with the disclosed embodiments, memory 326 may includeinstructions that, when executed by processor 324, perform one or moreprocesses consistent with the functionalities disclosed herein.Moreover, processor 324 may execute one or more programs locatedremotely from controller 300. For example, controller 300 may access oneor more remote programs, that, when executed, perform functions relatedto disclosed embodiments.

Controller 300 may also include a user interface 328. User interface 328may include a display, such as a cathode ray tube (CRT), a liquidcrystal display (LCD), or a touch screen, for displaying information toa computer user. For example, the display may be used to present thewafer inspection result (e.g., defect information, dimensioninformation, etc.) to a user. Interface 328 may also include an inputdevice, including alphanumeric and other keys, for communicatinginformation and command selections to processor 324. Another type ofuser input device is a cursor control, such as a mouse, a trackball, orcursor direction keys for communicating direction information andcommand selections to processor 328 and for controlling cursor movementon the display. The input device typically has two degrees of freedom intwo axes, a first axis (for example, x) and a second axis (for example,y), that allows the device to specify positions in a plane. In someembodiments, the same direction information and command selections ascursor control may be implemented via receiving touches on a touchscreen without a cursor. For example, a user may use the input device toselect an inspection area of a wafer or enter the defect properties tobe examined.

In some embodiments, user interface 328 may be configured to implement agraphical user interface (GUI) that may be stored in a mass storagedevice as executable software codes that are executed by the one or morecomputing devices. This and other modules may include, by way ofexample, components, such as software components, object-orientedsoftware components, class components and task components, processes,functions, fields, procedures, subroutines, segments of program code,drivers, firmware, microcode, circuitry, data, databases, datastructures, tables, arrays, and variables.

FIG. 7 is a flowchart of a wafer inspection method 700, consistent withembodiments of the present disclosure. Method 700 may be performed by acontroller (e.g., controller 300) that is in communication with an ebeamtool (e.g., ebeam tool 104). Referring to FIG. 7, method 700 may includeone or more of the following steps 710-740.

In step 710, the controller controls the ebeam tool to scan a wafer(e.g., wafer 203) with a primary electron beam (e.g., primary electronbeam 220). The scanning operation may be performed by deflecting theprimary electron beam over the wafer surface, moving the wafer under theprimary electron beam, or a combination thereof.

In step 720, while the primary electron beam scans the wafer, thecontroller receives an SE/BSE signal and an EBIC signal substantiallysimultaneously. Both the SE/BSE signal and EBIC signal result from thescanning. The ebeam tool may include an electron detector (e.g.,electron detector 206) for collecting the SE/BSE and generating anSE/BSE signal having an intensity that is proportional to the SE/BSEcurrent. The ebeam tool may also include an ammeter (e.g., electrondetector 232) for measuring the EBIC. Both the SE/BSE signal and EBICsignal are amplified and then transmitted to the controller.

In step 730, the controller correlates the SE/BSE signal to the EBICsignal. The controller may correlate each data point of the SE/BSEsignal and the EBIC signal to the corresponding scanning position.Alternatively or additionally, the controller may synchronize the SE/BSEsignal with the EBIC signal in time. Optionally, the controller mayconstruct an SE/BSE image or an EBIC image of the wafer based on theSE/BSE signal and EBIC signal, respectively.

In step 740, the controller determines structural information of thewafer based on at least one of the SE/BSE signal and the EBIC signal. Insome embodiments, the controller may compare the SE/BSE signaloriginating from different dies or cells of a wafer, and detect defectsbased on the comparison. For example, the controller may determinewhether the SE/BSE images of different dies or cells have anydiscrepancies. If there is a discrepancy, the controller may furtherreview the SE/BSE images to determine whether the discrepancycorresponds to a defect. Similarly, in some embodiments, the controllermay also compare the EBIC signal originating from different dies orcells of a wafer and detect defects based on the comparison.

In some embodiments, the controller may compare the SE/BSE signal (orimage) with the corresponding or synchronized EBIC signal (or image),and determine structural information of the wafer based on thecomparison. For example, the controller may detect a defect based on thecomparison. For example, for a structure or device (e.g., HAR structureor device) that has low SE/BSE intensity but high EBIC intensity (i.e.,the SE/BSE emission is lower than a predetermined threshold), the EBICsignal may be used to detect the defect because the EBIC signal has ahigher signal-to-noise ratio. For another example, the sum of the SE/BSEintensity and the EBIC intensity is generally equal to the intensity ofthe primary electron beam, which is a constant. If, however, the sum ofthe SE/BSE intensity and the EBIC intensity fluctuates drastically atcertain regions of the wafer, this phenomenon may suggest that theaffected region contains a defect.

The above-described system and method inspect a wafer based on bothSE/BSE imaging of the wafer and EBIC imaging of wafer. In particular,when the disclosed ebeam system scans a wafer and detects SEs and BSEsoriginating from the wafer, an additional data channel is created tosimultaneously collect EBIC (or substrate current) of the wafer. TheEBIC data may be correlated to (e.g., synchronized with) the SE/BSEdata, and used to supplement or substitute the SE/BSE data when theSE/BSE based measurement has low density to the inspected structures.

Because the EBIC data may be obtained and analyzed at the same time asthe SE/BSE data, while the wafer is scanned by an electron beam, thedisclosed system and method may be fully integrated into the in-linemetrology. Moreover, because the disclosed embodiments provide highersensitivity, additional post-production processes/steps to examine HARstructures may be avoided. Therefore, the productivity of ICmanufacturing is improved.

The embodiments may further be described using the following clauses:

-   1. An electron beam system comprising:

an electron detector that includes circuitry to detect secondaryelectrons or backscattered electrons (SE/BSE) emitted from a wafer;

a current detector that includes circuitry to detect anelectron-beam-induced current (EBIC) from the wafer; and

a controller having one or more processors and a memory, the controllerincluding circuitry to:

-   -   acquire data regarding the SE/BSE;    -   acquire data regarding the EBIC; and    -   determine structural information of the wafer based on an        evaluation of the SE/BSE data and the EBIC data.

-   2. The electron beam system of clause 1, wherein in the    determination of the structural information, the controller includes    circuitry to:

synchronize the SE/BSE data and the EBIC data.

-   3. The electron beam system of any one of clauses 1 and 2, wherein    in the determination of the structural information, the controller    includes circuitry to:

compare the SE/BSE data with the EBIC data; and

determine the structural information based on the comparison.

-   4. The electron beam system of clause 3, wherein in comparing the    SE/BSE data to the EBIC data, the controller includes circuitry to:

construct an SE/BSE image of the wafer based on the SE/BSE data;

construct an EBIC image of the wafer based on the EBIC data; and

compare the SE/BSE image to the EBIC image.

-   5. The electron beam system of any one of clauses 1 to 4, wherein    the structural information includes at least one of:

a defect on the wafer;

a critical dimension of a feature formed on the wafer; and

an edge of a feature formed on the wafer.

-   6. The electron beam system of any one of clauses 1 to 5, wherein    the current detector circuitry is coupled to the wafer, the current    detector circuitry being configured to receive electric current from    the wafer and provide EBIC data to the controller.-   7. The electron beam system of clause 6, wherein the current    detector circuitry coupled to the wafer includes an ammeter    configured to measure an intensity of the EBIC and output the    intensity as the EBIC data.-   8. The electron beam system of any one of clauses 6 and 7, the    current detector circuitry coupled to the wafer includes an    amplifier configured to amplify the EBIC data.-   9. The electron beam system of any one of clauses 1 to 8, wherein    the electron detector includes circuitry to provide SE/BSE data    based on intensity of the SE/BSE to the controller.-   10. The electron beam system of any one of clauses 1 to 9, wherein    the EBIC is substrate current of the wafer.-   11. The electron beam system of any one of clauses 1 to 10, further    comprising an electron beam tool that includes circuitry to scan the    wafer with a primary electron beam.-   12. A computer system comprising:

a memory storing instructions; and

a processor electronically coupled to the memory and configured toexecute the instructions to cause the computer system to:

-   -   acquire data regarding secondary electrons or backscattered        electrons (SE/BSE) emitted from a wafer;    -   acquire data regarding an electron-beam-induced current (EBIC)        from the wafer;    -   evaluate the SE/BSE data and the EBIC data; and    -   determine structural information of the wafer based on the        evaluation of the SE/BSE data and the EBIC data.

-   13. The computer system of clause 12, wherein in the determination    of the structural information, the processor is further configured    to execute the instructions to cause the computer system to:

compare the SE/BSE data with the EBIC data; and

determine the structural information based on the comparison.

-   14. The computer system of clause 13, wherein in comparing the    SE/BSE data with the EBIC data, the processor is further configured    to execute the instructions to cause the computer system to:

construct an SE/BSE image of the wafer based on the SE/BSE data;

construct an EBIC image of the wafer based on the EBIC data; and

compare the SE/BSE image with the EBIC image.

-   15. The computer system of any one of clauses 12 to 14, wherein the    structural information includes at least one of:

a defect on the wafer;

a critical dimension of a feature formed on the wafer; and

an edge of a feature formed on the wafer.

-   16. The computer system of any one of clauses 12 to 15, wherein the    EBIC is substrate current of the wafer.-   17. A method comprising:

acquiring data regarding secondary electrons or backscattered electrons(SE/BSE) emitted from a wafer scanned with an electron beam;

acquiring data regarding an electron-beam-induced current (EBIC) fromthe wafer; and

determining structural information of the wafer based on an evaluationof the SE/BSE data and the EBIC data.

-   18. The method of clause 17, further comprising:

synchronizing the SE/BSE data with the EBIC data.

-   19. The method of any one of clauses 17 and 18, wherein determining    the structural information of the wafer comprises:

comparing the SE/BSE data with the EBIC data; and

determining the structural information based on the comparison.

-   20. The method of clause 19, wherein comparing the SE/BSE data and    the EBIC data further comprises:

constructing an SE/BSE image of the wafer based on the SE/BSE data;

constructing an EBIC image of the wafer based on the EBIC data; and

comparing the SE/BSE image to the EBIC image.

-   21. The method of any one of clauses 17 to 20, further comprising:    receiving substrate current of the wafer and convert the substrate    current into the EBIC data.-   22. The method of clause 21, further comprising:

measuring an intensity of the substrate current and outputting theintensity as the EBIC data.

-   23. The method of any one of clauses 21 and 22, further comprising:

amplifying the EBIC data.

-   24. A non-transitory computer-readable medium storing a set of    instructions that is executable by one or more processors of one or    more devices to cause the one or more devices to perform a method    comprising:

acquiring data regarding secondary electrons or backscattered electrons(SE/BSE) emitted from a wafer;

acquiring data regarding an electron-beam-induced current (EBIC) fromthe wafer; and

determining structural information of the wafer based on an evaluationof the SE/BSE data and the EBIC data.

-   25. The non-transitory computer-readable medium of clause 24,    wherein the set of instructions is executable by the one or more    processors of one or more devices to cause the one or more devices    to further perform:

controlling an electron beam tool to scan the wafer using a primaryelectron beam.

-   26. The non-transitory computer-readable medium of any one of    clauses 24 and 25, wherein the set of instructions is executable by    the one or more processors of one or more devices to cause the one    or more devices to further perform:

synchronizing the SE/BSE data with the EBIC data.

-   27. The non-transitory computer-readable medium of any one of    clauses 24 to 26, wherein the set of instructions is executable by    the one or more processors of one or more devices to cause the one    or more devices to further perform:

comparing the SE/BSE data with the EBIC data; and

determining the structural information based on the comparison.

-   28. The non-transitory computer-readable medium of clause 27,    wherein the set of instructions is executable by the one or more    processors of one or more devices to cause the one or more devices    to further perform:

constructing an SE/BSE image of the wafer based on the SE/BSE data;

constructing an EBIC image of the wafer based on the EBIC data; and

comparing the SE/BSE image to the EBIC image.

-   29. The non-transitory computer-readable medium of any one of    clauses 24 to 28, wherein the EBIC is substrate current of the    wafer.    -   It will be appreciated that the disclosed embodiments are not        limited to the exact construction that has been described above        and illustrated in the accompanying drawings, and that various        modifications and changes may be made without departing from the        scope thereof. It is intended that the scope of the subject        matter should only be limited by the appended claims.

What is claimed is:
 1. An electron beam system comprising: an electrondetector configured to detect secondary electrons or backscatteredelectrons (SE/BSE) emitted from a wafer; a current detector configuredto detect an electron-beam-induced current (EBIC) from the wafer; and acontroller having one or more processors and a memory storinginstructions, the one or more processors being configured to execute theinstructions to cause the controller to: acquire data regarding theSE/BSE; acquire data regarding the EBIC; and determine structuralinformation of the wafer based on a comparison of the SE/BSE data andthe EBIC data.
 2. The electron beam system of claim 1, wherein in thedetermination of the structural information, the one or more processorsare configured to execute the instructions to cause the controller to:synchronize the SE/BSE data and the EBIC data.
 3. The electron beamsystem of claim 1, wherein in comparing the SE/BSE data to the EBICdata, the one or more processors are configured to execute theinstructions to cause the controller to: construct an SE/BSE image ofthe wafer based on the SE/BSE data; construct an EBIC image of the waferbased on the EBIC data; and compare the SE/BSE image to the EBIC image.4. The electron beam system of claim 1, wherein the structuralinformation includes at least one of: a defect on the wafer; a criticaldimension of a feature formed on the wafer; or an edge of a featureformed on the wafer.
 5. The electron beam system of claim 1, wherein thecurrent detector is coupled to the wafer, the current detector beingconfigured to receive electric current from the wafer and provide EBICdata to the controller.
 6. The electron beam system of claim 5, whereinthe current detector coupled to the wafer includes an ammeter configuredto measure an intensity of the EBIC and output the intensity as the EBICdata.
 7. The electron beam system of claim 5, the current detectorcoupled to the wafer includes an amplifier configured to amplify theEBIC data.
 8. The electron beam system of claim 1, wherein the electrondetector is configured to provide SE/BSE data based on intensity of theSE/BSE to the controller.
 9. The electron beam system of claim 1,wherein the current detector is coupled to a substrate of the wafer, thecurrent detector being configured to receive electric current from thesubstrate.
 10. The electron beam system of claim 1, further comprisingan electron beam tool configured to scan the wafer with a primaryelectron beam.
 11. The electron beam system of claim 1, wherein in thedetermination of the structural information, the one or more processorsare configured to execute the instructions to cause the controller todetect a defect on the wafer based on at least: a sum of an SE/BSEintensity and an EBIC intensity, or a difference between the SE/BSEintensity and the EBIC intensity.
 12. The electron beam system of claim11, wherein the one or more processors are configured to execute theinstructions to cause the controller to: detect a defect on the waferbased on a fluctuation of the sum of the SE/BSE intensity and the EBICintensity.
 13. The electron beam system of claim 11, wherein the one ormore processors are configured to execute the instructions to cause thecontroller to: in response to the EBIC intensity being higher than theSE/BSE intensity, detect a defect on the wafer based on the EBIC data.14. A method comprising: acquiring data regarding secondary electrons orbackscattered electrons (SE/BSE) emitted from a wafer scanned with anelectron beam; acquiring data regarding an electron-beam-induced current(EBIC) from the wafer; and determining structural information of thewafer based on a comparison of the SE/BSE data and the EBIC data. 15.The method of claim 14, further comprising: synchronizing the SE/BSEdata with the EBIC data.
 16. The method of claim 3, wherein comparingthe SE/BSE data and the EBIC data further comprises: constructing anSE/BSE image of the wafer based on the SE/BSE data; constructing an EBICimage of the wafer based on the EBIC data; and comparing the SE/BSEimage to the EBIC image.